In vehicles, it is known in the practice to transmit as needed to the drive wheels via a transmission a drive torque produced by a prime mover. If vehicles such as four-wheel passenger cars or four-wheel driven trucks are designed with several driven axles, the power of the prime mover in the power train of such vehicles has to be distributed to the individual drive axles.
For power distribution so-called differential transmissions are used wherein the longitudinal differentials seen in driving direction are used for longitudinal distribution of the input of the prime mover to several driven axles of a vehicle. So-called transverse differentials or differential gear units are used in relation to the travel direction of a vehicle for a transverse distribution of the input to drive wheels of a vehicle axle.
The designs of differential transmissions conventionally used in the practice are so-called bevel gear differentials, spur gear differentials in planetary construction or also worm gear differentials. Spur gear differentials are mostly used as longitudinal differentials due to the possibility of asymmetric torque distribution. Meanwhile bevel gear differentials represent a standard for transverse compensation in vehicles and worm gear differentials are used both for longitudinal distribution and for transverse distribution.
With the aid of those distributor transmissions, it is possible to distribute a drive torque in arbitrary ratios to several drive axles without producing stresses in a power train. In addition, it is obtained by using differential transmissions that drive wheels of a drive axle of a vehicle can be driven at different rotational speeds independently of each other according to the different path lengths of the left or right lane whereby the drive torque can be distributed to both drive wheels symmetrically and thus free of yaw torques.
However, opposed to these advantages is the disadvantage that the propulsion forces of two drive wheels of a vehicle axle or of two or more drive axles transmissible to the road, due to the compensating action of a differential transmission, depend on the slight or slightest transmissible drive torque of both drive wheels or of the drive axles. This means, for example, when a drive wheel spins, standing upon smooth ice, the other drive wheel is fed no torque higher than that fed to the spinning drive wheel even when it stands upon soil of good grip. In such a driving situation, the vehicle disadvantageously cannot start off due to the compensating action of a differential transmission which makes a rotational speed difference possible between two output shafts of a differential transmission.
In the practice, it has therefore been changed by adequate means to prevent compensating motion of a differential transmission in the presence of critical driving conditions. This is implemented, for example, by a differential lock known manually or mechanically activatable with mechanical, magnetic, pneumatic or hydraulic means which, by blockage of the differential transmission, locks up to 100% every compensating motion.
Also used are automatically locking differentials, also called differential transmissions with limited slip or locking differentials. Those differential transmissions make it possible to transmit a torque to a wheel of a vehicle axle or to a drive axle even if the other wheel or the other drive axle, in case of several drive axles, skids as a consequence of poor ground adhesion. At the same time, the advantage of the transmission of force free of yaw torque is lost and the free adaptation of the wheel rotational speeds of both drive wheels of a drive axle to the path lengths of the two lanes, likewise, is disadvantageously prevented.
It is further known from the practice to provide externally controlled differential brakes for adjusting a degree of the compensating action of a differential transmission. Those differential brakes constitute mostly electronically regulated and hydraulically actuated systems in which, depending on the existing travel condition, it is possible to a great extent to lock a normally non-locked or only weakly locked differential. An extent of the prevention of the compensating action of a differential transmission is adaptable via a control on the actually existing driving condition.
The previously mentioned solutions, however, have the disadvantage of being characterized by high control and regulation costs and besides require high constructional expenses due to the hydraulic system.
The problem, on which the invention is based, is to make a transmission for distribution of an as needed drive torque available to at least two output shafts, with which a starting off in critical driving situations is ensured and which has a simple and practical design, the same as being characterized by low control and regulation expenses.